In a medium bowl, whisk together flour, cinnamon, baking soda and salt.

In a large mixing bowl, beat together butter and sugar until combined. Beat in egg, followed by molasses, until smooth and well incorporated. Add flour mixture and mix just until combined.

Using a teaspoon cookie scoop, drop the dough onto parchment-lined baking sheets. Bake until the center of the cookies are dry to the touch, about 10 to 12 minutes. Remove and let sit on the baking sheets for about 1 to 2 minutes before transferring them to a wire rack to cool completely.

To make the filling

In a medium bowl, beat together butter and molasses until creamy. Add in confectioners' sugar and continue mixing until smooth and spreadable. Spread the filling, about a rounded teaspoonful, on the bottoms of half of the cookies. Place the remaining cookies on top.